Address transition and message correlation between networks nodes

ABSTRACT

The present invention relates to a method, system and network element for providing an address transition if a connection point at one end of a connection is changed from a first network node to a second network node of a cellular network. An address information and at least one alternative address information are transmitted in a signaling message from said first network node to said second network node. One of said address information and said alternative address information is selected at the second network node and used for re-establishing said connection towards the other end of said connection. Thereby, the new point of connection is allowed to re-establish the connection towards the other end of the connection, even if it can only communicate using one of the two addresses. Furthermore, signaling messages, e.g. messages relating to charging, lawful interception, and/or customized applications, received from different network nodes can be correlated based on the alternative addresses.

FIELD OF THE INVENTION

[0001] The present invention relates to a method, system and networkelement for providing an address transition, such as a transition froman IPv4 (Internet Protocol version 4) address to an IPv6 address,between a first network node and a second network node of a cellularnetwork, e.g. a GPRS (General Packet Radio Services) network, and/or amessage correlation.

BACKGROUND OF THE INVENTION

[0002] UMTS (Universal Mobile Telecommunications System) is a moregeneral term for the 3G, (third generation) telecommunications systembased on the WCDMA high capacity radio interface. GSM is the mostwidespread 2G (second generation) telecommunications system based onTDMA (Time Division Multiple Access) radio. The goal of the GPRS systemis to provide global layer 2 connectivity from a cellular mobileterminal (MT, sometimes also referred to as mobile station (MS) or userequipment (UE)) using 2G or 3G radio technology (e.g. GSM, AmericanTDMA, UMTS, GERAN (GSM/EDGE Radio Access Network) to an external packetdata network. GPRS can support various layer 3 protocols (e.g. IPv4;IPv6; PPP (Point-to-Point Protocol)).

[0003] The main nodes of a GPRS network are SGSN (Serving GPRS SupportNode) and GGSN (Gateway GPRS Support Node). SGSNs are the nodes servingthe MT. Each SGSN supports GPRS for GSM and/or UMTS. GGSNs are the nodehandling the interworking with PDNs (Packet Data Networks). Signalingand data are exchanged between SGSN and GGSN or SGSN and SGSN using theGTP (GPRS Tunneling Protocol) protocol. GTP protocol handles mobility,and creation, modification and deletion of GTP tunnels, as well astransfer of user data between GSNs. GTP allows multi-protocol packets tobe tunneled between GSNs and between an SGSN and the UMTS TerrestrialRadio Access Network (UTRAN, not shown) through which a connection tothe concerned MT is established. Other systems components need not beaware of the GTP. Typically, two IP addresses are used for a singletunnel, one for the GTP control message (i.e. signalling). and one forthe GTP user packet (i.e. carrying user data).

[0004] At GPRS attach, the SGSN establishes a mobility management (MM)context containing information pertaining to e.g. mobility and securityfor the concerned MT. At PDP context activation, the SGSN establishes aPDP context, to be used for routing purposes, with the GGSN thesubscriber will be using A GPRS attached mobile terminal (MT) can beassigned either a static or dynamic IP address (referred to also as PDPaddress). The static address is assigned by the Home Public Land MobileNetwork (HPLMN) operator at the time of subscription. The dynamic IPaddress can be allocated by a GGSN (Gateway GPRS Support Node) of eitherthe HPLMN or the visited PLMN (VPLMN) operator at PDP (Packet DateProtocol) context activation time. In addition to address allocation,the GGSN implements the forwarding of IP packets from a GTP (GPRSTunneling Protocol) tunnel to a packet data network (PDN) and viceversa. There are two kinds of PLMN backbone networks, an Intra-PLMNbackbone network and an Inter-PLMN backbone network. The Intra-PLMNbackbone network is a private IP network intended for packet domain dataand signaling within a PLMN only, while the Inter-PLMN backbone is usedfor roaming from one PLMN to another (via Border Gateways). Serving GPRSSupport Nodes (SGSNs) and GGSNs use the Intra-PLMN backbone to exchangeGPRS domain data and signalling.

[0005] During roaming, both the Intra-PLMN backbone of the home andvisited networks are used in addition to the Inter-PLMN backbone. When asubscriber is roaming to another PLMN, i.e. a VPLMN, the user needs tofirst attach to the network. In GPRS attach, the MT informs the ServingSGSN of its intention to connect to the network by giving informationabout its identity, capability and location. The SGSN then checks theMT's identity and performs an authentication procedure in order tosecure the transmission path. The attachment is completed after the SGSNhas received roaming subscriber data from the Home Location Register(HLR) of the subscriber's HPLMN and finished a location updateprocedure. After the GPRS attach, the MT sends an ‘Activate PDP context’request, in which the Access Point Name (APN) is a reference to the GGSNAccess Point (AP) to be used in either the home or visited PLMN. TheSGSN selects the GGSN based on a PDP context subscription record andsends the context data to a selected GGSN. The GGSN then routes thepackets to the appropriate Packet Data Networks (PDN).

[0006] When a subscriber is roaming in the VPLMN, there are thefollowing two possibilities for GGSN selection. Firstly, the homenetwork GGSN can be used via the Inter-PLMN backbone and BGs. The homeGGSN then routes the packets to their destination. Secondly, a visiteddomain GGSN can be used for routing the packets from the VPLMN to theirdestination directly through a packet data network (PDN), such as thepublic Internet.

[0007] It should be noted that there are two levels of IP addressing:

[0008] the user IP address corresponding to the packets carried over GTPprotocol. The corresponding IP address is referred to as PDP address oruser address; and

[0009] the network IP address corresponding to the packets carried belowGTP protocol. The corresponding IP addresses are the node IP addressesused to exchange GTP packets between GSNs. These IP addresses might alsobe used for network operation such as charging or O&M.

[0010] User and network addresses are independent of each other thanksto the GTP protocol, and could both be either IPv4 or IPv6.

[0011] The GPRS backbone nodes of the second (2G) and third (3G)generation may optionally use an IPv6 based addressing for networkaddresses. However,.existing specifications allowing the use of IPv6addresses, do not define how to maintain backward compatibility withIPv4 based nodes. An SGSN should know in advance that the GGSN selectedsupports IPv6 addresses before inserting an IPv6 address e.g. in acreate PDP context request message.

[0012] Furthermore, another problem arises with the known procedures. Ifa MT moves from an IPv6 capable SGSN connected to an IPv6 capable GGSNto an IPv4 only SGSN, the communication will get lost as the new SGSNcannot use the IPv6 address transferred. Such a scenario is veryrealistic in particular when two operators with equipment from differentmanufacturers (or just different software release) have roamingagreements (e.g. national roaming). It should be noted that existingIPv4-to-IPv6 transition mechanisms do not apply here as they do notaffect IP addresses carried in GTP.

[0013] In addition, a practical requirement is that the protocol changeshave to be done so that-nodes based on older version of specifications(and so not supporting enhancement proposed here), have to continueinterworking with new nodes supporting the proposed enhancement proposedhere.

SUMMARY OF THE INVENTION

[0014] It is therefore an object of the present invention to provide amethod and system for providing an address transition or correlationfunction, by means of which backward address compatibility can beachieved.

[0015] This object is achieved by a method and system as claimed inclaims 1, 13, 17 and 19, respectively.

[0016] Additionally, the above object is achieved by a network node asclaimed in claims 23, 27 and 30, respectively.

[0017] Accordingly, if one of the point of connection is changed (e.g.Inter SGSN Routing area update; Serving RNC relocation), the old pointof connection (e.g. old SGSN) shall send to the new point of connection(e.g. new SGSN) both first and second address, in order to allow the newpoint of connection to re-establish the connection towards the other endof the connection (GGSN), even if it can only communicate using one ofthe 2 addresses.

[0018] Furthermore, signaling messages, e.g. messages relating tocharging, lawful interception, and/or customized applications (e.g.Customized Applications for Mobile network Enhanced Logik (CAMEL)architecture), received from different network nodes can be correlatedbased on the alternative addresses.

[0019] Advantageous further developments are defined in the dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, the present invention will be described ingreater detail based on a preferred embodiment with reference to theaccompanying drawings, in which:

[0021]FIG. 1 shows a schematic block diagram of a GPRS backbone networkarchitecture, in which the present invention can be implemented;

[0022]FIG. 2 shows a signaling diagram indicating indicating anInter-SGSN routing area update procedure according to the preferredembodiment, and

[0023]FIG. 3 shows a signaling diagram indicating a Serving SRNSRelocation procedure according to the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The preferred embodiment will now be described based on a packetdomain PLMN backbone network architecture as indicated in FIG. 1, inwhich an IPv6 to IPv4 address transition mechanism is used.

[0025] According to FIG. 1, a packet data network (PDN) 10 (e.g. an IPnetwork) is connected via a first GGSN 31 to a first PLMN 71 comprisinga first Intra-PLMN backbone network 51. Furthermore, the first PLMN 71includes at least a first SGSN 61 and a second SGSN 62 connected to eachother and to the first GGSN 31 through the first Intra-PLMN backbonenetwork 51. Additionally, the PDN 10 is connected to each other via asecond GGSN 32 to a second PLMN 72 comprising a second Intra-PLMNbackbone network 52. Furthermore, the second PLMN 72 includes at least athird SGSN 63 connected to the second GGSN 32 through the secondIntra-PLMN backbone network 52. The first and second PLMNs 71, 71 areconnected to each other via an Inter-PLMN backbone network 20. Theconnection between the first PLMN 71 and the Inter-PLMN backbone network20 is provided through a first border gateway (BG) 41. Similarly, theconnection between the second PLMN 72 and the Inter-PLMN backbonenetwork 20 is provided through a second BG 42.

[0026] Each of the Intra-PLMN backbone networks 51, 52 may be a privateIP network intended for packet domain data and signaling. A private IPnetwork is an IP network to which some access control mechanism isapplied in order to achieve a required level of security. The Inter-PLMNbackbone network 20 can be packet data network, e.g. the public Internetor a leased line, which may be selected by a roaming agreement includinga BG security functionality (i.e. typically just a router with securityfunctions). The first and second BGs 41, 42 are not defined within thescope of the packet domain.

[0027] The GPRS Support Nodes (GSNs), i.e. the first to third SGSNs 61to 63 and the first and second GGSNs 31, 32, contain functionalityrequired to support GPRS functionality for GSM (Global System for Mobilecommunication) and/or UMTS. In particular, the first and second GGSNs31, 31 represent network nodes which are accessed by the PDN 10 due toevaluation of the PDP address. It contains routing information for GPRSattached users: The routing information is used to tunnel packet dataunits (PDUs) to the MT's current point of attachment, i.e. therespective Serving SGSN. Thus, the first and second GGSNs 31, 32 are thefirst point of PDN interconnection with the first and second PLMNs 71,72, respectively. The first to third SGSNs 61 to 63 represent nodes forserving the MT. Each SGSN supports GPRS for GSM and/or UMTS.

[0028] Further details regarding the network architecture and signalingprocedures can be gathered from the 3GPP (3rd Generation PartnershipProject) specification TS 23.060 Release 4.

[0029] According to the preferred embodiment, an SGSN willing to use anIPv6 addressing will always indicate IPv6 and also IPv4 SGSN addressesin a respective GTP, signaling message used to request creation of a GTPtunnel to the selected GGSN. Optionally, the SGSN may also indicate IPv6and also IPv4 SGSN addresses in a respective GTP signaling message usedto request update of a GTP tunnel. But this is not necessary if beforesending the update, the SGSN already knows the type of addressessupported by GGSN. It may however be useful if the operator like toconfigure on a node by node basis the technology to be used (may be dueto intermediate network).

[0030] If the selected GGSN supports IPv6 in the network plane, it shallalso indicate IPv6 addresses in the corresponding GTP response messagetogether with IPv4 addresses. The IPv4 addresses are stored in the SGSNand not used for transmission. IPv6 addresses are used for transmissionon the network plane. In case of an inter SGSN handover, IPv4 and IPv6addresses shall be given to the new SGSN in a backward compatible way.If the new SGSN does not support IPv6 addresses, it uses the obtainedIPv4 addresses to update the tunnel towards the GGSN. Also the GGSN maystart receiving user data from the new SGSN before the tunnel has beenupdated. Therefore the-first and second GGSNs 31, 32 shall be ready toreceive GTP packets (signaling or user data) on either IPv4 or IPv6addresses.

[0031] It should be noted, that in future a new SGSN may be provided,which is capable of using only IPv6 on network plane, and sameprinciples would apply.

[0032] As an implementation alternative, the node could select thetransmission technology (IPv4 or IPv6) to be used based on operatorconfiguration

[0033] If the selected GGSN does not support IPv6 in the network plane,it indicates only IPv4 addresses in the corresponding GTP responsemessage. IPv4 addresses are then used for transmission on the networkplane as currently defined.

[0034] Because it is proposed to send the IPv6 address as a new optionalinformation element, backward compatibility can be provided so as tointroduce IPv6 in future network nodes and maintain connections on thenetwork plan even if a new SGSN supports only IPv4.

[0035] In the following, examples for specific signaling messages andthe incorporation of a specific address field for transmitting analternative address will be described with reference to FIGS. 2 and 3.Specific details regarding the signaling messages and procedures can begathered from the 3GPP specifications TS 29.060 and TS 23.060 Release 4.

[0036] A Create PDP Context Request is sent from a SGSN node to a GGSNnode as a part of the GPRS PDP Context Activation procedure. A validrequest initiates the creation of a tunnel between a PDP Context in aSGSN and a PDP Context in a GGSN. If the SGSN prefers to use IPv6 belowGTP, it include the IPv6 addresses in new message fields AlternativeSGSN Address, and an alternative or equivalent IPv4 address in existingmessage fields SGSN address. If the GGSN supports IPv6 below GTP, itstores and uses the alternative IPv6 SGSN addresses for communicationwith the SGSN. If the GGSN supports only IPv4 below GTP, it stores anduses the IPv4 SGSN addresses for communication with the SGSN. The SGSNaccepts packets whether they are sent to its IPv4 or IPv6 address. TheGGSN should not store SGSN IP addresses that it does not use. Thismechanism provides maximum flexibility, as it is not based on specialDNS features, and allows the GGSN to have processes using IPv4 only andprocesses using both IPv4 and IPv6.

[0037] The following Table 1 shows the specific information elementsprovided in the Create PDP Context Request message. TABLE 1 InformationPresence element requirement IMSI Conditional Recovery OptionalSelection mode Conditional Tunnel Endpoint Identifier Data MandatoryTunnel Endpoint Identifier Control Plane Conditional NSAPI MandatoryLinked NSAPI Conditional Charging Characteristics Optional TraceReference Optional Trace Type Optional End User Address ConditionalAccess Point Name Conditional Protocol Configuration Options ConditionalSGSN Address for signalling Mandatory SGSN Address for user trafficMandatory Alternative SGSN Address for signalling Optional AlternativeSGSN Address for user traffic Optional MSISDN Conditional Quality ofService Profile Mandatory TFT Conditional Trigger Id Optional OMCIdentity Optional Private Extension Optional

[0038] The Create PDP Context Response message is sent from the GGSNnode to the SGSN node as a response of a Create PDP Context Request.When the SGSN receives the Create PDP Context Response with the Causevalue indicating ‘Request Accepted’, the SGSN activates the PDP contextand may start to forward PDUs to/from the MT from/to the external datanetwork.

[0039] If the GGSN supports IPv6 below GTP, and the SGSN included anIPv6 SGSN address in the request, the GGSN shall include the IPv6addresses in the new fields Alternative GGSN Address, and an equivalentIPv4 address in the fields GGSN address. The SGSN uses the alternativeIPv6 GGSN addresses for communication with the GGSN, except if theoperator has configured the use of IPv4. The SGSN stores the GGSNaddresses and sends them to a new SGSN in a PDP context response message(message sent by old-SGSN to new SGSN, after an MS has performed aRouting area update procedure to a new SGSN, that the new SGSN has senta PDP context request message to the old SGSN). The GGSN shall acceptpackets whether they are sent to its IPv4 or IPv6 address. Thismechanism avoids losing connection if the new SGSN support IPv4 onlybelow GTP.

[0040] Table 2 shows specific information elements provided in theCreate PDP Context Response message. TABLE 2 Information elementPresence requirement Cause Mandatory Reordering required ConditionalRecovery Optional Tunnel Endpoint Identifier Data Conditional TunnelEndpoint Identifier Control Plane Conditional Charging ID ConditionalEnd User Address Conditional Protocol Configuration Options OptionalGGSN Address for Control Plane Conditional GGSN Address for user trafficConditional Alternative GGSN Address for Control Plane ConditionalAlternative GGSN Address for user traffic Conditional Quality of ServiceProfile Conditional Charging Gateway Address Optional Private ExtensionOptional

[0041] Furthermore, an Update PDP Context Request message is sent from aSGSN to a GGSN as part of the GPRS Inter SGSN Routing Update procedureor the PDP Context Modification procedure or to redistribute contextsdue to load sharing. The SGSN may-use SGSN IPv6 addresses only if it hasreceived an IPv6 GGSN address from an old SGSN (Inter SGSN Routing AreaUpdate case) or GGSN (PDP context modification). Otherwise SGSN usesSGSN IPv4 addresses.

[0042] If the GGSN supports IPv6 below GTP, and the SGSN included anIPv6 SGSN address in the request, the GGSN includes the IPv6 addressesin the fields Alternative GGSN Address, and an equivalent IPv4 addressin the fields GGSN address. The SGSN uses the alternative IPv6 GGSNaddresses for communication with the GGSN. The SGSN may store both IPv4and IPv6 GGSN addresses and send them to a new SGSN in PDP contextresponse message. The GGSN alternative address fields are not sent ifthe GGSN address field is not sent. This mechanism guarantees that theSGSN always stores proper IPv4 and IPv6 GGSN addresses, so thatconnection will not be lost if moving to a new SGSN supporting only IPv4below GTP.

[0043] In the following Table 3, specific information elements in theUpdate PDP Context Response message are shown. TABLE 3 Informationelement Presence requirement Cause Mandatory Recovery Optional TunnelEndpoint Identifier Data Conditional Tunnel Endpoint Identifier ControlPlane Conditional Charging ID Conditional GGSN Address for Control PlaneConditional GGSN Address for User Traffic Conditional Alternative GGSNAddress for Control Plane Conditional Alternative GGSN Address for usertraffic Conditional Quality of Service Profile Conditional ChargingGateway Address Optional Private Extension Optional

[0044] Furthermore, as regards the SGSN Context Request message, the newSGSN sends this message to the old SGSN to get the mobility management(MM) and PDP Contexts for the MT. The old SGSN responds with an SGSNContext Response.

[0045] The new SGSN adds an SGSN Address for the control plane. If thenew SGSN supports IPv6 below GTP, it adds its IPv6 address in the fieldAlternative SGSN Address for Control Plane. The old SGSN then selectsthe SGSN address for Control Plane depending on its IPv6 supports, andstores this selected SGSN Address and uses it when sending control planemessages for the MT to the new SGSN in the SGSN context transferprocedure.

[0046] Table 4 shows specific information elements provided in the SGSNContext Request message. TABLE 4 Information element Presencerequirement IMSI Conditional Routing Area Identity (RAI) MandatoryTemporary Logical Link Identifier (TLLI) Conditional Packet TMSI(P-TMSI) Conditional P-TMSI Signature Conditional MS Validated OptionalTunnel Endpoint Identifier Control Plane Mandatory SGSN Address forControl Plane Mandatory Alternative SGSN Address for Control ConditionalPlane Private Extension Optional

[0047] The old SGSN sends an SGSN Context Response message to the newSGSN as a response to a previous SGSN Context Request. The old SGSN mayuse SGSN IPv6 addresses only if it received IPv6 SGSN address from thenew SGSN. Otherwise SGSN shall use SGSN IPv4 addresses.

[0048] The new SGSN sends an SGSN Context Acknowledge message to the oldSGSN as a response to the SGSN Context Response message. Only afterreceiving the SGSN Context Acknowledge message, the old SGSN starts toforward user data packets. SGSN Context Acknowledge indicates to the oldSGSN that the new SGSN has correctly received PDP Context informationand is ready to receive user data packets.

[0049] The new SGSN uses an SGSN Address for user traffic, which maydiffer from that provided by the underlying network service (e.g. IP).The old SGSN stores this SGSN Address and uses it when sending downlinkPDUs to the new SGSN for the MT. The SGSN may use IPv6 addresses only ifit received IPv6 SGSN address for control plane from the old SGSN.Otherwise the SGSN use SGSN IPv4 addresses.

[0050]FIG. 2 shows a signaling diagram indicating an Inter-SGSN routingarea update procedure according to the preferred embodiment.

[0051] In this signaling example, the MT sends a Routing Area UpdateRequest to a new SGSN, so as to initiate a routing area update. Inresponse thereto, the new SGSN sends an SGSN Context Request messageincluding the SGSN Address fields and the Alternative SGSN Addressfields to the old SGSN. In response thereto, the old SGSN returns anSGSN Context Response message in which the desired address type is setin the SGSN Address for Control Plane fields, and all GGSN IPv4 and IPv6addresses are included if available. The new SGSN responds with an SGSNContext Acknowledge message including the used address type information.Then, the new SGSN sends an Update PDP Context Request message includingthe set address type information to the respective GGSN. This message issent using a GGSN IP address received from old SGSN. If the new SGSN andGGSN support IPv6 on the network plane, the IPv6 address of GGSN ispreferably used. If either SGSN or GGSN does not support IPv6, IPv4addresses are used. Here, it is assumed that in a first phase oftransition towards IPv6, all nodes support IPv4. The GGSN returns anUpdate PDP Context Response message including the GGSN Address fieldsand the Alternative GGSN Address fields. These address fields areespecially necessary in the following cases:

[0052] The old SGSN supported only IPv4, and had not stored thealternative GGSN address, so that the new SGSN needs to receive it fromGGSN to be able to use IPv6 for the connection

[0053] The GGSN has changed its IP address (typically due to areallocation of the PDP context to a new processing card)

[0054] In addition, if for some reason, the GGSN is configured to use.IPv4 to communicate towards the new SGSN (due to possible problem inintermediate IP network), the GGSN will return only the IPv4 addressesand will not send an alternative address field containing the IPv6address.

[0055] Finally, the required routing area update procedure is performed.

[0056] As a further GTP signalling message, a Forward Relocation Requestmessage is defined, which is sent by an old SGSN to a new SGSN to conveynecessary information to perform an SRNS (Serving Radio NetworkSubsystem) relocation procedure between the new SGSN and a target RNC(Radio Network Controller) of the UTRAN. In this case, the old SGSN addsan SGSN Address for Control Plane field information. If the old SGSNsupports IPv6 below GTP, it adds its IPv6 address in this fieldAlternative SGSN Address for Control Plane. The new SGSN selects theSGSN address for Control Plane depending on its IPv6 supports, andstores this selected SGSN address and uses it when sending control planemessages for the MT to the old SGSN in the SRNS relocation procedure.

[0057] Table 5 shows specific information elements provided in theForward Relocation Request message. TABLE 5 Information element Presencerequirement IMSI Mandatory Tunnel Endpoint Identifier Control PlaneMandatory RANAP Cause Mandatory MM Context Mandatory PDP ContextConditional SGSN Address for Control plane Mandatory Alternative SGSNAddress for Control plane Optional Target Identification Mandatory UTRANtransparent container Mandatory Private Extension Optional

[0058] The new SGSN sends a Forward Relocation Response message to theold SGSN as a response to a previous Forward Relocation Request message.The new SGSN adds an SGSN Address for Control Plane information. TheSGSN may insert IPv6 addresses only if it received an IPv6 SGSN addressfor control plane from the-old SGSN. Otherwise the new SGSN uses SGSNIPv4 addresses. The old SGSN stores this SGSN address and uses it whensending control plane messages for the MT to the new SGSN in the SRNSrelocation procedure. FIG. 3 shows a signaling diagram indicating anSRNS (Serving Radio Network Subsystem) relocation procedure according tothe preferred embodiment.

[0059] In this signaling example, a source SRNS of the UTRAN decides toperform or initiate an SRNS relocation and sends a Relocation Requiredmessage to the old SGSN. In response thereto, the old SGSN determines ifthe SRNS relocation is an inter-SGSN SRNS relocation and, if so, itsends a Forward Relocation Request message including the SGSN Addressfield and the Alternative SGSN Address field for control plane signalingto the respective new SGSN. In response thereto, the new SGSN send aRelocation Request message to the target Radio Network Controller (RNC)of the UTRAN. Then, the lu bearers of the radio access bearers (RABS)are setup between the target RNC and the new SGSN as the existing radiobearers will be reallocated between the MT-and the target RNC when thetarget RNC takes the role of the Serving RNC in the new SRNS. After thenew SGSN has received the Relocation Request Acknowledgement messagefrom the UTRAN, the GTP tunnels are established between the target RNCand the new SGSN. Then, the Forward Relocation Response message is sentfrom the new SGSN to the old SGSN to thereby indicate that the targetRNC is ready to receive from the source SRNC (Serving RNC) of the SRNSthe forwarded packet data units (PDUs). The old SGSN continues the SRNSrelocation by sending a Relocation Command message to the source SRNC.The source SRNC is now ready to forward downlink user data directly tothe target RNC. When the data forwarding is completed, the target RNCsend a relocation Detect message to the new SGSN. In response thereto,the new SGSN sends an Update PDP Context Request message to a concernedGGSN. The GGSN returns an Update PDP Context Response message includingthe GGSN Address fields and the Alternative GGSN Address fields. Whenthe new SGSN receives a Relocation Complete message from the SRNC, aForward Relocation Complete signaling is exchanged between the new andthe old SGSNs, and then the old SGSN initiates an lu release procedureat the SRNC. Finally, if the new Routing Area Identification isdifferent, the MT initiates a Routing Area Update procedure.

[0060] Furthermore, a PDP Context information element contains theSession Management parameters, defined for an external packet datanetwork address, that are necessary to transfer between SGSNs at theInter SGSN Routing Area Update procedure.

[0061] If the GGSN negotiated the use of IPv6 below GTP with the oldSGSN, the old SGSN sets Alternative GGSN Address for User Traffic andAlternative GGSN Address for Control Plane fields to contain the IPv6addresses to be used to communicate with the GGSN. A new SGSN notsupporting IPv6 below GTP ignores these alternative GGSN addresses, anduses for communication the GGSN Address for User Traffic and GGSNAddress for Control Plane fields. A new SGSN supporting IPv6 below GTPstores the-GGSN Address for User Traffic and GGSN Address for ControlPlane, but uses use for communication the Alternative GGSN Address forUser Traffic and Alternative GGSN Address for Control Plane.

[0062] In Table 6, a PDP Context information field is shown. TABLE 6 1Type = 130 (Decimal) 2-3 Length 4 Res- VAA Res- Order NSAPI erved erved5 X X X X SAPI 6 QoS Sub Length 7 − (q + 6) QoS Sub [4 . . . 255] Q + 7QoS Req Length (q + 8)-(2q + 7) QoS Req [4 . . . 255] 2q + 8 QoS Neg.Length (2q + 9)-(3q + 8) QoS Neg [4 . . . 255] (3q + 9)-(3q + 10)Sequence Number Down (SND)¹⁾ (3q + 11)-(3q + 12) Sequence Number Up(SNU)¹⁾ 3q + 13 Send N-PDU Number¹⁾ 3q + 14 Receive N-PDU Number¹⁾ (3q +15)-(3q + 18) Uplink Tunnel Endpoint Identifier Control Plane (3q +19)-(3q + 22) Uplink Tunnel Endpoint Identifier Data I 3q + 23 PDPContext Identifier 3q + 24 Spare PDP Type 1 1 1 1 Organisation 3q + 25PDP Type Number 3q + 26 PDP Address Length (3q + 27) − m PDP Address [1. . . 63] M + 1 GGSN Address for control plane Length (m + 2) − n GGSNAddress for control plane [4 . . . 16] N + 1 GGSN Address for UserTraffic Length (n + 2) − o GGSN Address for User Traffic [4 . . . 16]O + 1 APN length (o + 2) − p APN P + 1 Spare (sent Transaction as 0 0 00) Identifier P + 2 Transaction Identifier Alternative GGSN Address forcontrol plane Length Alternative GGSN Address for control plane [4 . . .16] Alternative GGSN Address for User Traffic Length Alternative GGSNAddress for User Traffic [4 . . . 16]

[0063] If having either IPv6 or IPv4 address in GGSN Address for ControlPlane is allowed, GGSN Address for Control Plane of the PDP contextinformation field may sometimes be an IPv6 address and sometimes an IPv4address during an active PDP context. This may happen e.g. if GGSNindicates IPv6 address in GGSN Address for Control Plane and IPv4address in Alternative GGSN Address for Control Plane at PDP contextactivation, whereas an old SGSN indicates IPv4 address in GGSN Addressfor Control Plane to a new SGSN at routing area update. In this case,GGSN Address for Control Plane is the same in GGSN and old SGSN, whereasGGSN Address for Control Plane is different in new SGSN. In this case,e.g. charging correlation by using GGSN Address for Control Plane doesnot work.

[0064] According to the preferred embodiment, a GGSN supporting bothIPv6 and IPv4 adds both IPv6 address and IPv4 address to CDRs (CallDetailed Records) created for a PDP context, i.e. to G-CDRs. The SGSNmay add either one IP address, i.e. GGSN Address for Control Plane, ortwo IP addresses, i.e. GGSN Address for Control Plane and AlternativeGGSN Address for Control Plane, to the CDRs created for the PDP context,i.e. to S-CDRs. This way, it is possible for the CGF (Charging GatewayFunctionality) to correlate CDRs created by the GGSN (including bothIPv6 address and IPv4 address) and CDRs created by the SGSN(s)(including either one IP address, IPv6 or IPv4, or including both IPv6address and IPv4 address).

[0065] In addition to charging, correlation may be needed e.g. forlawful interception or CAMEL messages or information. In general, anymessage or information generated by multiple nodes can be correlatedbased on the address and alternative address information. For lawfulinterception correlation, GGSN sends both IPv6 address and IPv4 address,whereas SGSN may send either one IP address, i.e. GGSN Address forControl Plane, or two IP addresses, i.e. GGSN Address for Control Planeand Alternative GGSN Address for Control Plane. GGSN thus sends bothIPv6 address and IPv4 address, whereas SGSN may send either IPv6 addressor IPv4 address or both for lawful interception correlation. This way,it is possible to correlate e.g. lawful interception information createdby GGSN for the PDP context and lawful interception information createdby SGSN(s) for the PDP context.

[0066] It is noted that the present invention can be implemented in anycellular network to provide address backward compatibility or messagecorrelation function, when an address information is transferred betweennetwork nodes. The names of the various functional entities, signalingmessages and information elements used in the context of the preferredembodiment are not intended to limit or restrict the invention. Thepreferred embodiments may thus vary within the scope of the attachedclaims.

1. A method for providing an address or network transition if a connection point at one end of a connection is changed from a first network node to a second network node of a cellular network, said method comprising the steps of: a) transmitting an address information and at least one alternative address information in a signaling message from said first network node to said second network node; b) selecting one of said address information and said alternative address information at said second network node; and c) using said selected address information for re-establishing said connection towards a third node at the other end of said connection.
 2. A method according to claim 1, wherein, when establishing said connection, possible addresses to be used for this connection are transmitted as said address information and said at least one alternative address information in a signaling message from said first network node to said third network node, and addresses of said third node are stored in said first network node.
 3. A method according to claim 1, where said address information can be used to address a node according to an old addressing or network, used before the transition, and said alternative address information can be used to address a node according to the new addressing or network.
 4. A method according to claim 1, wherein said signaling message is sent as part of a location or routing area update message or a relocation procedure.
 5. A method according to claim 1, wherein said signaling message is a GTP message.
 6. A method according to claim 1, wherein said first and second network nodes are SGSNs, and said third network node is a GGSN.
 7. A method according to claim 1, wherein said address information and said alternative address information are a user and/or network addresses.
 8. A method according to claim 7, wherein said address information and said alternative address information are IPv4 or IPv6 addresses.
 9. A method according to claim 1, wherein said address information and said alternative address information are transmitted in respective predetermined fields of said signaling message.
 10. A method according to claim 9, wherein said predetermined fields are provided in a PDP context information field.
 11. A method according to claim 1, wherein said alternative address information is coded as an optional information so that a network node not supporting said alternative address information ignores it.
 12. A method according to claim 11, wherein said connection is re-established with an old addressing mechanism based on said address information if said second node ignores said alternative address information.
 13. A method for providing a message correlation function in a data network, said method comprising the steps of: a) adding an address information and at least one alternative address information to a message at a first network node; b) selecting one of said address information and said alternative address information at a second network node to which said message has been routed; and c) using said selected address information for correlating said message to a message received from a third network node.
 14. A method according to claim 13, wherein said message is a call record for charging purposes.
 15. A method according to claim 13, wherein said second network node is a charging gateway functionality.
 16. A method according to claim 13, wherein said message is a lawful interception information or an information of a customized application.
 17. A system providing an address or network transition, said system comprising: a) a first network node for transmitting an address information and at least one alternative address information in a signaling message if a connection point at one end of a connection is changed from said first network node; and b) a second network node for receiving said signaling message if said connection point is changed to said second network node, for selecting one of said address information and said alternative address information, and for using said selected address information for re-establishing said connection towards a third network node at the other end of said connection.
 18. A system according to claim 17, wherein said first and second network nodes are SGSNs of a GPRS backbone network, and wherein said third network node is a GGSN of said GPRS backbone network.
 19. A system for providing a message correlation function in a data network, said system comprising: a) a first network node for adding an address information and at least one alternative address information to a message; b) a second network node for receiving said selecting one of said address information and said alternative address information to which said message has been routed; and c) using said selected address information for correlating said message to a message received from a third network node.
 20. A system according to claim 19, wherein said message is a call record for charging purposes.
 21. A system according to claim 19, wherein said second network node has a charging gateway functionality.
 22. A system according to claim 19, wherein said message is a lawful interception information or an information of a customized application.
 23. A network node of a cellular network, said network node being arranged to transmit an address information and at least one alternative address information in a signaling message, if a connection point at one end of a connection is changed from said network node to another network node.
 24. A network node according to claim 23, where said transmitted address information and said at least one alternative address information is used to reestablish said connection towards a third node.
 25. A network node according to claim 24, wherein said network node is adapted to store said address information and said alternative address information in order to be used to address said third network node.
 26. A network node according to claim 23, wherein said network node is an SGSN.
 27. A network node of a cellular network, said network node being arranged to receive a message if a connection point at one end of a connection is changed from another network node to said network node, to select one of an address information and an alternative address information provided in said message, and to use said selected address information for re-establishing said connection towards a third network node at the other end of said connection.
 28. A network node according to claim 27, wherein said network node is adapted to receive data and/or signaling either on said address information or on said alternative address information.
 29. A network node according to claim 27, wherein said network node is a GGSN.
 30. A network node of a cellular network, said network node being arranged to receive a message if a connection point at one end of a connection is changed from another network node to said network node, to select one of an address information and an alternative address information provided in said message, and to use said selected address information for correlating said message to a message received from a third network node.
 31. A network node according to claim 30, wherein said network node has a charging gateway functionality, and said signaling message is a charge record.
 32. A network node according to claim 30, wherein said message is a lawful interception information or an information of a customized application. 